1. Field of the Invention
The present invention relates to a lamp, and more particularly, to an external electrode fluorescent lamp and a manufacturing method thereof that increase the external surface area of the electrode.
2. Discussion of the Related Art
Nowadays, image display devices are developed from cathode ray tubes (CRTs) into liquid crystal display (LCD) devices and plasma display panel (PDP) devices. LCD devices have been spotlighted as the next generation display because they have advantages characteristics, such as small size, light-weight, and low power consumption, and they do not generate harmful electromagnetic waves.
In general, an LCD device includes a lower substrate having a thin film transistor (TFT) formed thereon, an upper substrate having color filters arranged thereon, and a liquid crystal layer injected into a gap between the lower and upper substrates. For example, the TFT receives and transmits control signals to generate an electric field, and an alignment of liquid crystal molecules in the liquid crystal layer is changed in accordance with the electric field, thereby altering a light transmittance thereof. As a result, a color image is displayed using the liquid crystal molecules having a refractive anisotropy and a dielectric anisotropy and passing light through the color filters.
Because an LCD device cannot generate light by itself, the LCD device also includes a backlight unit for emitting light toward a liquid crystal display panel. Backlight units are classified into an edge type and a direct type according to the position of a light source relative to a display plane. In particular, the direct type backlight unit has a high light efficiency, imposes no limitation in the size of an image display surface and can be easily handled. Thus, the direct type backlight unit is widely used for a large-sized LCD device, e.g., an LCD device of more than 30 inches.
The direct type backlight unit does not require a light guide for converting linear light from a lamp into plane light. Instead, a direct type backlight unit includes a plurality of lamps provided at a lower portion of the display plane, a reflection sheet for reflecting light from the lamp to the display plane to prevent light loss, and a diffuser plate for scattering the light to an upper side of the lamps to emit light uniformly. The lamps include one of a point light source, such as an incandescent lamp and a white halogen lamp, a linear light source, such as a hot cathode fluorescent lamp (HCFL), a cold cathode fluorescent lamp (CCFL), and an external electrode fluorescent lamp (EEFL), and a planar light source, such as light emitting diodes (LEDs) in a matrix shape.
Currently, cold cathode fluorescent lamps (CCFLs) are widely used, but external electrode florescent lamps (EEFLs) are gradually replacing the CCFL. Since an EEFL has brightness of more than 400 nit, which is 60% greater than brightness of a CCFL, the EEFL can expand the TFT-LCD application field such as TV. In addition, unlike a CCFL having electrodes within lamps, an EEFL has external electrodes and thus is advantageous in operating in parallel, such that a uniform brightness can be realized by reducing a voltage deviation between the lamps. Further, inverters that are required for driving a plurality of EEFLs can be reduced because EEFLs can be driven by a multi-driving method. As a result, the number of parts of the backlight unit is reduced, and the manufacturing cost and the weight of the LCD module can be remarkably reduced.
FIG. 1 is a plane view illustrating a direct type backlight unit of an LCD device according to the related art. In FIG. 1, a direct type backlight unit 1 includes a plurality of external electrode fluorescent lamps (EEFLs) 11 for emitting light and an inverter 21 for driving the lamps 11. Each of the lamps 11 includes external electrodes 13 and 15 formed respectively at both ends thereof. The external electrodes 13 and 15 are connected to the inverter 21 through one of common electrodes 17 and 19 and through one of lamp wires 23. Thus, a voltage from the inverter 21 is applied through the lamp wires 23 to the common electrodes 17 and 19 to the lamp 11, and a current flows due to a discharge between glass layers (dielectric layers) of the lamp 11. In addition, the current can be controlled and the respective lamps 11 can be simultaneous turned on/off, thereby enabling a multi-driving thereof.
FIG. 2 is a cross-sectional view illustrating an EEFL of the backlight unit shown in FIG. 1 during an emission. As shown in FIG. 2, the external electrodes 13 and 15 are respectively formed on external surfaces of end portions of the lamp 11. When an AC voltage is applied to the external electrodes 13 and 15, an electric field is generated inside the lamp 11. The generated electric field then causes plasma to be generated inside the lamp 11. As a result, the generated plasma causes charges to accumulate on an inner surface of the lamp 11 corresponding to the external electrodes 13 and 15, and such charges cause a magnetic discharge to occur.
In particular, when a high frequency and high voltage is applied to the lamp 11, a strong electric field can be generated at the external electrodes 13 and 15. Such a generated electric field excites gas in the lamp 11, causing UV rays to be emitted. The emitted UV rays then excite a fluorescent material within the lamp 11, thereby causing light emission.
However, when an EEFL is used in a large-size LCD device, e.g., an LCD device of 30-inch or larger, such an EEFL must be long. Thus, the EEFL requires an even higher driving voltage to generate a sufficient electric field to emit light, thereby resulting in difficulty when using the EEFL.